1. Field of the Invention
The present invention relates to an airbag device, which comprises an airbag to be folded and housed and an inflator for feeding an inflating gas into the airbag.
2. Description of Related Art
In the prior art, the airbag device of this kind is known, as disclosed in Unexamined Published Japanese Patent Application No. 149199/1995. The airbag device disclosed is used in the steering wheel of a vehicle.
The airbag of this airbag device is provided with two circular wall portions, i.e., a side facing the engine (facing the steering wheel) and a wall portion facing the passenger (or the driver). Moreover, the airbag is formed by sewing the circumference of the vehicle front-facing wall portion and of the passenger-facing wall portion to each other. In the vehicle front-facing wall portion, on the other hand, there is opened a gas inlet port for admitting an inflating gas from an inflator. In the vehicle front-facing wall portion, moreover, there is arranged a flow regulating cloth for clogging the gas inlet port. This flow regulating cloth regulates the flow of the inflating gas flowing from the gas inlet port to limit the protruding motion of the passenger-facing wall portion of the airbag to the passenger (or the driver) passenger-facing wall portion. This airbag can expand widely while inflating in the flow direction of the inflating gas so that it is difficult for it to apply an unnecessary pushing force to the approaching passenger.
In the airbag thus constructed, however, the flow of the inflating gas is regulated from the beginning to the completion of inflation by the flow regulating cloth. In other words, the flow of the inflating gas is regulated until just before the completion of inflation by the flow regulating cloth. In the airbag device having the aforementioned construction, therefore, there is room for improvement in shortening the time period from the beginning to the completion of inflation of the airbag. This is because it is desired that the inflating gas flow freely from the gas inlet port into the airbag without being regulated in its flow in the time period before the completion of inflation of the airbag as to shorten the time required for the airbag to completely inflate.
On the other hand, an airbag device for a steering wheel, having an airbag arranged the flow regulating cloth therein, is exemplified by International Laid-Open No. WO97/36768. In the airbag device of this laid-open application, the airbag is so folded at two stages and housed in the steering wheel so that the vehicle front-facing wall portion and the driver-facing wall portion are folded flat so that their edges come toward the gas inlet port.
In the airbag device of the above-specified laid-open application, the flow regulating cloth in the airbag regulates the inflow of the inflating gas into the airbag body to go in two directions, i.e., to the front and to the back. In the folding of the airbag, at the first stage, the left and right side portions of the airbag are folded to approach the gas inlet port so that the two folds line up with each other on the left and right. At the second stage, the respective portions of the edges of the two folded portions of the first stage projecting forward and located at the rear are folded so as to also bring these folded portions closer to the gas inlet port. In short, at the second stage, the two new folded portions line up with each other at the forward and rear.
When the inflating gas flows into the airbag body, moreover, the airbag is expanded and inflated to complete the inflation while opening the folds of the second stage and the first stage.
If the portion of the driver-facing wall portion directly opposite the gas inlet port is raised at the beginning of inflation of the airbag by the inflating gas, however, the airbag device thus constructed is expanded to unfold at the two folded portions of the second stage. Simultaneously with this, moreover, the two folded portions of the first stage are also unfolded to separate from each other. This is because the portions of the airbag on the right and left sides are folded at the first stage so as to form two folded portions lined up with each other on the right and left. Moreover, the unfolding of the two folded portions of the first stage is the expansion to the left and right, thereby to obstruct the flow regulating effect of the flow regulating member. Specifically, the airbag device of the aforementioned construction has room for improvement in that its effect to regulate the flow of the inflating gas by the flow regulating cloth arranged in the airbag body, allowing the airbag to expand widely and quickly in the regulating direction of the inflating gas.
In the airbag device, on the other hand, it is has been proposed that a construction made by inflating an auxiliary inflation portion arranged in the airbag at the beginning of inflation in low temperatures would provide protection for the passenger.
One known airbag device of this kind is Unexamined Published Japanese Patent Application No. 8-119052. The disclosed airbag device is used in the steering wheel of a vehicle.
In the airbag of this airbag device, the vehicle front-facing wall portion and the passenger-facing wall portion are sewn to each other with a rupturable sewing thread so as to surround the gas inlet port spaced away from the outer edge of the wall portions. In the portion surrounded by this sewing location, moreover, there is arranged the auxiliary inflation portion communicating with the gas inlet port.
In this airbag, even at a low temperature where the inflating gas which enters is of a small volume, the passenger (or the driver) to interfere at the beginning of inflation at the low temperature can be protected at the beginning of inflation by the auxiliary inflation portion. This is because inflating gas is made to flow into the auxiliary inflation portion with a smaller capacity than that of the airbag body, raising the internal pressure and so completing the inflation.
In the airbag of the aforementioned Patent Application, however, the sewn junction of the vehicle front-facing wall portion and the passenger-facing wall portion formed on the outer edge of the auxiliary inflation portion is ruptured when the inflation of the airbag itself is completed to enlarge the capacity for a cushioning action. As a result, it is difficult to maintain the airbag at a predetermined internal pressure and to complete the inflation. This is because the holes passed by the sewing thread in the vehicle front-facing wall portion and the passenger-facing wall portion may be enlarged and leak the inflating gas when the sewing thread of the sewn portions is ruptured. Especially at low temperature, the aforementioned problems are serious because it is difficult to maintain the internal pressure by the inflating gas can.
Therefore, the airbag of the Patent Application is provided at the sewn portion with measures for applying a sealing material so that the gas may not leak from the sewn portion. Thus, the airbag production has an increased number of steps of which raises the cost.
On the other hand, the airbag device of this kind is desired to expand and inflate the airbag by regulating the inflow of the inflating gas so as to suppress the unnecessary protrusion to the passenger.
Therefore, there is known an airbag device having a construction, as disclosed in Unexamined Published Japanese Patent Application No. 104196/1996. In this airbag device, a flow regulating cloth for closing the gas inlet port is arranged at the vehicle front-facing wall portion in the airbag. This flow regulating cloth regulates the inflow of the inflating gas from the gas inlet port thereby to suppress the protrusion of the passenger-facing wall portion in the airbag toward the passenger. Moreover, the flow regulating cloth is so sewn near its center that it can be separated from the passenger-facing wall portion.
In this airbag, from the beginning to a point midway in inflation, the protrusion of the portion of the passenger-facing wall portion directly opposite the gas inlet port is prevented from extending to the passenger by the joining of the flow regulating cloth to the passenger-facing wall portion. Moreover, the airbag is enabled to extend its width through the flow of the inflating gas in the directions as guided by the flow regulating cloth, and then the junction of the flow regulating cloth to the passenger-facing wall portion is released, thereby completing the inflation.
In the airbag of the aforementioned Patent Application, however, there remains room left for improvement, because the unnecessary protrusion of the passenger-facing wall portion to the driver (or the passenger) cannot be avoided after the junction of the flow regulating cloth to the passenger-facing wall portion is released. This is because the airbag of the Patent Application is not provided with a regulating member for regulating the shape at the completion of inflation.
In case the airbag device of this kind is arranged in the steering wheel, moreover, it is desired that the abdomen of the driver be properly protected when the airbag is expanded and inflated.
Therefore, there is known an airbag device having a construction, as disclosed in Unexamined Published Japanese Utility Model Application No. 1007/1994. In this airbag device, tethers for regulating the shape of an airbag at the completion of inflation are arranged in the airbag. However, the airbag is inflated into an expanded shape that protrudes away from the engine toward the abdomen of the driver at the completion of inflation.
In the airbag device of the aforementioned Utility Model Application, however, the airbag that has completed its inflation protrudes away from the engine toward the abdomen of the driver but at the beginning of inflation of the airbag there is no control of its shape. Usually in the airbag device of this kind, in order to protect the driver properly, it is necessary to expand the airbag to quickly provide a thick cushion immediately after the beginning of inflation of the airbag between the rear-most (lower) portion of the steering wheel and the abdomen of the driver. This is because the steering wheel is positioned in proximity to the driver when the inflator acts.